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WMO/ITU Seminar Use of Radio Spectrum for Meteorology Earth ExplorationEarth Exploration--Satellite Service Satellite Service

(EESS)(EESS)-- Active Spaceborne Remote Active Spaceborne Remote Sensing and OperationsSensing and Operations

Bryan Huneycutt (USA) Charles Wende (USA)

WMO, Geneva, Switzerland16-18 September 2009

SRTM

Seawinds TRMM CloudsatJASONRadarsat

WMO/ITU Seminar Use of Radio Spectrum for Meteorology Active Sensor DefinitionActive Sensor Definition

Active Sensor:

an instrument which obtains information by the transmission and reception of radio waves.

WMO/ITU Seminar Use of Radio Spectrum for Meteorology Active Sensor TypesActive Sensor Types

• SYNTHETIC APERTURE RADARS – Cross-track looking sensors (one side only) which collect phase and delay time of coherent radar echoes; typical products include radar images and topographical maps of the Earth's surface.

• ALTIMETERS – Downward looking sensors measuring the precise echo delay time to extract the precise altitude of the ocean's surface.

• SCATTEROMETERS - Sensors looking at various aspects to the sides of the nadir track, measuring the return echo power variation with aspect angle to determine wind direction and speed on the ocean surface or return echo on the land surface.

• PRECIPITATION RADARS – Cross-track looking sensors measuring the radar echo returned from rainfall to determine the rainfall rate.

• CLOUD PROFILE RADARS – Downward-looking sensors measuring the radar echo returned from clouds to determine cloud reflectivity profile.

WMO/ITU Seminar Use of Radio Spectrum for Meteorology Active Sensor TypesActive Sensor Types

Notes: “[...]” are past missions, “(...)” are future missions.

WMO/ITU Seminar Use of Radio Spectrum for Meteorology

Synthetic Aperture Radars Synthetic Aperture Radars (SARs)(SARs)

• Provide radar images and by combining 2 images:- from different orbits →topographical maps of the Earth’s surface, or- taken at different times →maps indicating ground movement ~ centimeters

(Interferometric SAR, or InSAR)

• RF center frequency depends on the Earth’s interaction with the EM field- lower frequencies (< 2 GHz) penetrate vegetation and reflect off the ground- higher frequencies reflect off water (rain, vegetation, etc.)

• RF bandwidth affects the resolution of the image pixels

• Allowable image pixel quality degradation determines allowable interference level


SARs (cont.)SARs (cont.)

The Radarsat image (right) shows two flooded areas in north central Bulgaria in early June 2005 with respect to the reference Landsat image (left).



Los Angeles - SRTMwith Landsat Overlay

California-Height as color

SRTM DEM's



InSAR Image of the MaunaLoa Caldera in Hawaii

Ground motion indicatesDangerous undergroundvolcanic activity



RADARSAT-1 viewingIce off NewfoundlandAnd Labrador, Canada

WMO/ITU Seminar Use of Radio Spectrum for Meteorology AltimetersAltimeters

(a)

(b)

(c)

(d) tr td

t

t

t t

t2t1

• Provide altitude of the Earth’s ocean surface

• RF center frequency depends on the ocean surface interaction with the EM field

• Dual frequency operation allows ionospheric delay compensation

• JASON-1 uses frequencies around 13.6 GHz and 5.3 GHz

• Allowable height accuracy degradation determines the allowable interference level Illustration of Altimeter Return

WMO/ITU Seminar Use of Radio Spectrum for Meteorology Altimeters (cont.)Altimeters (cont.)


ScatterometersScatterometers• Provide the wind direction and speed over the ocean surface

• RF center frequency depends on the ocean surface interaction with the EM field and its variation over aspect angle

• Narrow RF signal bandwidth provides the needed measurement cell resolution

• Allowable wind speed accuracy degradation determines the allowable interference level

0 40 80 120 150 200 240 280 320 360

30

15

10

5

0

5.5 ms Horizontal Polarization 5.5 ms Vertical Polarization12.8 ms Horizontal Polarization12.8 ms Vertical Polarization

-1

-1

-1

-1

12.8 ms-1

5.5 ms-1

HH

HH

VV

VV

Azimuth Angle (degrees)

Rad

io s

catte

ring

Coe

ffici

ent (

dB)

Variation of Backscatter with Aspect

Angle


Ocean scatterometersOcean scatterometersSub-Satellite

Track

Sub-SatellitePoint

MonitorCells

175km

175km

600 km 600 km

Left Wind VectorSwath

Right Wind VectorSwath

-45o

-65o

-135o

135o

115o

45o

Sea WindsOrbit Track

800 km

Nadir Track

Cross Track

250 to 800 km Swath*

900 km

700 km

Nadir

46 Degree Beam

40 deg

NSCAT illuminated the Earth’s surface at several different fixed aspect angles

SEAWINDS scanning pencil beam illuminates scans at two different look angles from nadir, and scans 360 degrees about nadir in azimuth


Scatterometers (contd)Scatterometers (contd)


Scatterometers (cont.)Scatterometers (cont.)

Polar-orbiting scatterometersobserve oceanover the entireworld.

SeaWINDS on QuikSCAT provided these data.


Land scatterometersLand scatterometers

Aquarius scatterometer will illuminate the Earth’s surface at several different fixed aspect/nadir angle combinations

SMAP scatterometer scanning pencil beam illuminates scans at fixed look angle from nadir, and scans 360 degrees about nadir in azimuth


Scatterometers (cont.)Scatterometers (cont.)

Scatterometer looking at land – wet areas (blue) reflect back signals.


Precipitation RadarsPrecipitation Radars• Provide precipitation rate over the Earth’s

surface, typically concentrating on rainfall in the tropics

• RF center frequency depends on the precipitation interaction with the EM field


• Tropical Rainfall Measurement Mission (TRMM) uses only 0.6 MHz RF bandwidth

• Allowable minimum precipitation reflectivity degradation determines the allowable interference level


Precip. RadarsPrecip. Radars (cont.)(cont.)

The TRMM image shows the precipitation profile of the hurricane Ernesto on 26 August, 2006, revealing several deep convective towers (shown in red) that top out over 15km.


Cloud Profile RadarsCloud Profile Radars• Provide three dimension profile of cloud

reflectivity over the Earth’s surface• RF center frequency depends on the ocean

surface interaction with the EM field and its variation over aspect angle

• Antennas with very low sidelobes so as to isolate the cloud return from the higher surface return illuminated by the sidelobes


• Allowable reflectivity accuracy degradation determines the allowable interference level


Cloud Profilers (cont.)Cloud Profilers (cont.)

NOAA’s GOES (top) showed Hurricane Ileana on Aug 23, 2006.

CloudSat's Cloud Profiling Radar produced profiles of Ileana's clouds (bottom).


You have seen a variety of data products

today's instruments can produce.

Many* are available in a timely manner.

Use them to your country's advantage.

* some instruments are being demonstrated and are not in operational use.


And you can help -

Remind your administration that these useful

instruments operate in allocated frequency bands

and are given protection from interference.


ANNEX

Additional details about the technques


Active Sensor Active Sensor CharacteristicsCharacteristics

Characteristics Sensor Types

SAR Altimeter Scatterometer PrecipitationRadar

Cloud Radar

ViewingGeometry

Side-looking@20-55 deg offnadir

Nadir-looking

(1) Three/six fanbeams in azimuth(2) One/twoconical scanningbeams

Nadir-looking Nadir-looking

Footprint/Dynamics

(1) Fixed toone side

(2) ScanSAR

Fixed atnadir

(1) Fixed inazimuth

(2) Scanning

Scanning acrossnadir track

Fixed at nadir

Antenna Beam Fan beam Pencil beam (1) Fan beams

(2) Pencil beams

Pencil beam Pencil beam

Radiated PeakPower

1500-8000 W 20 W 100-5000 W 600 W 1000-1500 W

Waveform Linear FMpulses

Linear FMpulses

Interrupted CW,Short Pulses, orlinear FM pulses

Short pulses Short pulses

SpectrumWidth

20-450 MHz 320 MHz 5- 80 kHz, 1-4MHz

0.6 MHz 300 kHz

Duty Factor 1-5 % 46 % 10-31 % 2 % 1-14 %

Service Area Land/coastal/Ocean Ocean/Ice Ocean/Ice/Land Land/Ocean Land/Ocean


Repeat Cycles, Swath Repeat Cycles, Swath Width and Orbital Width and Orbital

Characteristics for EESS Characteristics for EESS (active)(active)

Table of Orbital Characteristics of Active Spaceborne Sensors

Sensors Repeat Cycle(days)

Altitude (km) Swath Width (km) Inclination (deg)

SARsRadarSAT-1/2

PALSARERS-1/2JERS-1/2ALMAZASAR

TerraSAR-L/X

16/2446

3,35,168/3544/35

33518

790692785580300800514

500 max70

102.510045

406 max200 max/ 100

98.598.298.598.073

98.5597.4

AltimetersJASON-1/2

RA2Topex/Poseidon

103510

13367801336

2616-20

75

6698.566

ScatterometersSeaWindsERS-1/2NSCATASCAT

RA-2

235412935

803780800835800

18005001400360100

98.298.598.698.798.55

Precipitation RadarsTRMM

GPM DPR49

0.125 (3 hrs for core & 8-10 LEOs)

350400

220125-245

3566

Cloud RadarCloudsat 16 705 1-2 98.2


Active Sensors Applications Active Sensors Applications by Sensor Typeby Sensor Type

Active SensorType

Active Sensor Applications

SARS SARs can provide knowledge of deep and undercanopy soil moisture which is critical for several Earth sci-ence disciplines and public welfare and policy making processes. These applications include, but are not lim-ited to: long-term weather forecasts, studying the long- and short-term climate variations through quantifyingelements of the energy and water cycle, for Carbon cycle science studies, and for studies and management ofunderground water resources and aquifers.

AtimetersThe data obtained by radar altimeters will be used to study ocean dynamics and their effects on climatologyand meteorology. Dual frequency altimeters also operate at 5.3 GHz to provide data to compensate for uncer-tainties in height measurements caused by ionospheric effects on the 13.5 GHz measurement. The radar alti-meter will provide precise measurements of the distance from the satellite to the Earth’s surface and also ofthe power and the shape of the returned echoes from ocean, ice and land surfaces, eventually allowing us toimprove our knowledge of climatology and environmental change detection.

Scatterometers Ocean scatterometers will measure surface wind speeds and directions over at least 90% of the oceans everytwo days in all weather and cloud conditions. Winds are a crit ical factor in determining regional weather pat-terns and global climate. Land scatterometers will measure surface echo returns to augment passive measure-ments of soil moisture and sea salinity. Scatterometers will play a key role in scientists efforts to understandand predict complex global weather patterns and climate systems.

PrecipitationRadars

One precipitation radar is the first space mission dedicated to measuring tropical and subtropical rainfall us-ing several microwave and visible/infrared sensors. Major objectives of the PR are 1) to provide a 3-dimen-sional rainfall structure, 2) to achieve quantitative rainfall measurement over land as well as over ocean, and3) to improve the accuracy of a microwave imager measurement by providing the rain structure information.

Cloud ProfilingRadars

The cloud profiling radar has been widely recognized as a key sensor to measure global distribution ofclouds, which is a critical issue in understanding the cloud role in earth’s radiation budget and thereby pre-dicting the global warming. The objective of spaceborne CPR is to measure global three –dimensional clouddistribution. The clouds which always cover about half area of the whole earth surface, play a significant andcomplicated role in the earth’s radiation budget. Especially, the vertical structure of clouds is a critical para-meter to decide whether clouds contribute to warming or cooling of the atmosphere.

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